Nearly three weeks after a temperature fluctuation at University Hospitals Fertility Clinic in Cleveland may have affected thousands of frozen eggs and embryos stored there, the clinic is finally telling patients what really happened, NPR reports.

In a letter sent to affected patients this week, per NPR, hospital officials explain that the remote alarm system on the tank storing the eggs and embryos, which was designed to alert staff if there were temperature issues, was off throughout the weekend of the fluctuation. "We don't know who turned off the remote alarm nor do we know how long it was off, but it appears to have been off for a period of time," the letter reads. "We are still seeking those answers." The letter says that the tank was also in need of maintenance work, and that staff had already been preparing for that work to take place shortly before the tank failure.

The letter also reveals that "many more eggs and embryos were affected than first estimated and it's unlikely that any are viable." In fact, the letter says, about 950 patients were affected by the storage tank failure and the total number of affected eggs and embryos is over 4,000. Originally, they estimated that about 2,000 eggs and embryos had been affected and they weren't sure how many of them were still viable.

Finally, in a video posted to the University Hospitals Facebook page this week, Tom Zenty, CEO of University Hospitals, said that the hospital will refund affected patients' storage fees and offer them individualized emotional and medical support.

Obviously, there's no way to replace what patients lost in the tank failure. But, hopefully, knowing more about the issues that took place can help patients as they process what's happened. "We know many families want and need the fertility services we provide," Zenty said in the video, "and we're committed to making the changes that will allow them to turn to us again with confidence."

Original report, March 15, 2018:

When you freeze your eggs or undergo IVF, it’s only natural to assume that those eggs or embryos will be kept safe until you’re ready to use them. Unfortunately, that isn’t the case for some patients who used a fertility clinic in Ohio.

Last week, officials with University Hospitals Fertility Clinic in Cleveland announced that an “unexpected temperature fluctuation” within the storage bank "impacted" several embryos.

At this point, they haven't been able to verify "the viability of all of the stored eggs and embryos,” Patti DePompei, R.N., M.S.N., President of UH Rainbow Babies & Children’s Hospital and UH MacDonald Women’s Hospital, said in a Facebook video, before apologizing to patients.

Kim Fatica, a publicist for University Hospitals Cleveland Medical Center, directed SELF to a statement published on the organization’s website last week. “We are investigating a recent incident at our Fertility Clinic involving an unexpected temperature fluctuation with the tissue storage bank where eggs and embryos are stored in liquid nitrogen,” the statement says. “At this time, we don’t yet know the viability of these eggs and embryos.” An investigation with external experts is being conducted, the statement adds.

“Right now, our patients come first,” the statement continues. “We are incredibly sorry this happened. We are committed to getting answers and working with patients individually to address their concerns. We have already initiated contact with all of our patients to inform them and respond to their questions, and set up a designated call center to arrange personal meetings or calls with their physicians.” Fatica also confirmed to SELF that more than 2,000 eggs and embryos may not be viable after the temperature fluctuation.

With so much uncertainty, patients are obviously going through a lot right now. Even under the best of circumstances freezing your eggs or embryos isn't a guarantee that you'll become pregnant later on, and the success of the procedure depends on your age, how many eggs or embryos you store, any medical conditions you have, and plenty of other factors during the IVF process. But if you're paying the money to store them (which could be over $1,000 for one year depending on where you are), you'd expect that they'd at least be safe.

So, aside from the financial concerns, the idea of losing eggs or embryos is devastating. At least two proposed class action lawsuits have been filed against the clinic, Cleveland.com reports.

Oddly enough, this wasn't the only fertility malfunction that day: The Pacific Fertility Center in San Francisco reported a temperature issue on the same day when a piece of equipment at the clinic's storage unit lost liquid nitrogen for a “brief period of time,” CNN reports.

This news is, understandably, anxiety-inducing for anyone who has embryos or eggs in a storage facility. However, experts stress that events like this are really rare.

While this news is devastating, it’s also incredibly rare for something like this to happen, Eve Feinberg, M.D., a reproductive endocrinologist with Northwestern Medical Group and an assistant professor at Northwestern University’s Feinberg School of Medicine, tells SELF. In fact, these are the only two malfunctions she's heard of in decades. “It’s unfortunate that two catastrophes happened at the same time, but, overall, embryo and egg storage is incredibly safe,” she says. “People should not panic.”

Kevin Doody, M.D., immediate past president of the Society for Assisted Reproductive Technology and director of CARE Fertility in Dallas/Ft. Worth, agrees, telling SELF that it’s “absolutely unbelievable” that something like this would happen in two locations at one time. He says he's not aware of any other incidents like this ever occurring.

Eggs and embryos are stored in a specific way, and clinics tend to follow the same procedures to ensure that they’re safe.

Once your eggs are extracted or embryos are created and you want them frozen for a later time, they’re stored in tanks at -196 degrees Celsius (about -384 degrees Fahrenheit), Michael Alper, M.D., a reproductive endocrinologist at Boston IVF, tells SELF.

The tanks are filled with liquid nitrogen to keep them cool, and they have alarms that go off in the event that the temperature dips below a set number, he explains. Clinics also check on their tanks on a regular basis to make sure they're intact and have proper liquid nitrogen levels, he says. Although every clinic has its own specific protocol, the overall process is basically the same for all of them, Dr. Feinberg says. “Clinics always have somebody available in case there’s a fluctuation in temperature to refill the tank with liquid nitrogen to make sure there aren’t fluctuations,” she says.

Eggs and embryos are sensitive, and temperature fluctuations can damage them.

There isn't an exact number at which the temperature becomes a problem, but Dr. Alper says that it's commonly accepted that there may be thaw damage once the temperature gets warmer than -150 degrees Celsius. That number isn't a hard line though, he says.

Unfortunately, there’s no way for doctors to know if an embryo or egg has been damaged until they’re thawed for use, Dr. Feinberg says. “We can’t test embryos beforehand,” she says. To find out if an embryo is viable, it would have to go through the thawing process, meaning that the patient would have to be prepared for the embryo transfer.

That thawing process is different from just letting the embryo sit out and warm up. Instead, frozen embryos and eggs are put in a series of solutions to thaw them at the right temperature and make sure that everything is still intact, Dr. Doody says.

How can patients know their eggs and embryos will be safe when shopping for a fertility clinic?

Although the practice of freezing eggs has become increasingly popular in recent years, the vast majority of people aren't thawing them (in one study of 1,468 women who froze their eggs, only 9 percent returned to use them). So, right off the bat, you'll want to see if the clinic you're looking at has both frozen and thawed eggs before. "Most clinics never have," Jake Anderson-Bialis, co-founder of FertilityIQ, a site that compiles data about fertility treatments and clinics, tells SELF. If they have, you also want to ensure that the clinic has at least an 80 percent "oocyte cryosurvival rate," meaning that 80 percent of the eggs that they freeze survive the thawing stage intact, he says.

Embryos, however, are a different story. "Most every clinic now commonly freezes and thaws embryos," Anderson-Bialis says. "You should expect most clinics to successfully thaw 95 percent of the embryos they freeze."

If you're planning on freezing your eggs, it's also important to make sure the clinic also has a good reputation for IVF, given that there's a very good chance that's where you're going to go through the process down the road. IVF is a more complex process than freezing eggs, Anderson-Bialis says, so it's important to do your homework. As for making sure your frozen eggs and embryos stay frozen, you'll want to make sure the clinic has back-up power and redundancy if the power cuts off. "Nearly all do, including the clinics that have been recently impacted," Anderson-Bialis says. "So while that is necessary, it's not sufficient."

According to Anderson-Bialis, you should look for a clinic that's a member of the Society for Assisted Reproductive Technology and accredited by the College of American Pathologists. And, because there are no best practices that fertility clinics are required to follow, he says it's crucial for you to ask questions. "You need to know your stuff, be on your game and be ready to ask the right questions to make you haven't turned [over] your hope, your savings, and your mental sanity to a place that's unworthy," he says.

Fertility experts are upset about this, too, and that’s probably a good thing.

“All of the physicians in the field, we’re just very saddened by this,” Dr. Feinberg says. “My heart really goes out to the families that are affected.” Dr. Alper agrees, calling the incidents "frightening experiences."

Fertility clinics across the country already work hard to make sure something like this won’t happen, but Dr. Doody expects that these incidents will make everyone revisit their own policies. “All the IVF clinics across the country will be looking at their procedures, alarm systems, redundancy, and everything that’s involved with preventing this sort of thing,” he says. “I can understand how patients might be worried, but it’s likely to become even more rare after this catastrophe.”